The purpose of our research has been to improve the magnetic properties of powders for plastic bonded magnet. Here powders were produced by water-atomization instead of cast-crushing method as usual. An optimum heat treatment for promotion of spinodal decomposition was obtained at 1000-1100K for a few minutes. Under these conditions, the magnetic properties were wholly improved, which were superior to cast-crushed powders. Practically the coercive force of both low-Co and high-Co water-atomized powders showed more than 600Oe and 1000Oe, respectively. Furthermore the additions of Co and Al were found to be effective for improvement of coercive force of both low-Co and High-Co powders. Water-atomization and

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Magnetostriction in isotropic magnet was studied by the of strain-gauge method. The results obtained were as follows: An increase in Co generally causes an increase in magnetostriction, except in some cases of heat-treatment. In the measurement of magnetostriction dependent upon Ni content for a basic material, an unusual change which was not correspondent to the change of magnetic properties was detected. The change of magnetostriction due to aging-treatment is not simple. However it is supposed from these results that there is in all probability another mechanism which was comfirmed for anisotropic magnet, 5, by the authors in the precipitation in isotropic magnet, too.

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A novel signal processing method based on calibration is present in this paper to improve the resolution of quadrature encoder. A radial magnetizing ring is adhered to rotor of motor, while six Hall ICs are placed around the evenly. magnetic filed produced by the can be sensed. Quadrature encoder is calibrated previously to get the table using a higher resolution optical encoder off-line. A quadrature encoder is designed and its resolution can achieve to 13-bits. Structure is very simple and cost is very low compare with an optical encoder. It can be used in unfavorable environment where a high-accuracy position detecting must be realized.

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The magnetic microstructure of 5 and 8 and their magnetization process were investigated systematically at a nanometer scale by means of electron holography and Lorentz microscopy. In particular, the magnetization process in alloys was visualized for the first time by utilizing a sharp magnetic needle made of sintered Nd₂Fe₁₄B in a transmission electron microscope. It was found that the direction of lines of magnetic flux changed at the boundaries between the α₁ and α₂ phases which were aligned in the direction of the magnetic field applied in the thermomagnetic treatment. In the Lorentz microscope image, these boundaries were observed as white lines and black bands, whose shapes reflected the difference in the shape anisotropy between 5 and 8. With an increase in the magnetic field induced by the magnetic needle, the magnetization direction of the domains magnetized in the direction opposite to that of the approaching needle was reversed, and finally a large reversed domain was formed. In both 5 and 8, it was shown that the magnetization process was accomplished through an entire magnetization reversal in each grain of the α₁ phase.

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Magnetostrictions in 5 magnet were measured by means of a strain gauge. Magnetostriction remarkably depends on the direction of heat-treatment in magnetic field—tendency similar to that in other metals. Then by aging at 600°C, magnetostriction decreases on the whole at a direction perpendicular to the field of heat-treatment in magnetic field and in heat-treatment without magnetic field, and conversely, increases at a direction parallel to the field treatment. This is an interesting phenomenon for discussion of the structure of such materials. A faster cooling after fusion causes an increase in magnetostriction. The starting ponit of magnetostriction curve shifts to the side of lower magnetizing force, which is a property in soft magnetic material. In this state, powder patterns can be observed. A heating at 900°C, or a temperature between 1000° and 1200°C at which γ phase is produced, causes a magnetostriction curve distinctly different from that after heating at 950° or 1300°C which are solution temperatures.

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We developed a low cobalt composition -type magnet having the magnetic properties equivalent to -5 (MK-5) magnet. An energy product of (BH)_<max>=4.94 MGOe, coercive force of H_c=647 Oe, and remanence of B_r=12.45 kG were achieved in a 20%Co alloy adding 0.8% of Nb.

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Effects of sulphur addition on the structure and magnetic properties of type alloys containing titanium were studied. type alloys containing 1 to 5% titanium could be converted into a columnar crystal structure by the addition of sulphur. Consequently, the residual induction amounts to 10100 G, the coercive force 1350 Oe, and the maximum energy product 7.2 M.G.Oe in 8 magnet alloy.
The columnar crystals of type alloys containing titanium are smaller in diameter than those of 5. For example, the columnar structure of 6 (1.2%Ti) contains 150 to 400 crystals per 1 cm² of the cross section, while in 5, merely some tens of crystals.
The residual induction, 11000 G in the columnar 7 and 10000 G to 10500 G in the columnar 8, is not affected by sulphur addition. The coercive forces of columnar 7 and 8 containing about 0.2% sulphur are 1100 Oe and 1350 Oe respectively, but they fall down with the increasing sulphur content.
The amount of sulphur remaining in the solidified alloys is smaller than that initially added, and the loss of added sulphur through casting and freezing becomes greater as the amount of sulphur addition becomes large.
Microstructures of sulphur added Alnicos show needle or rod-shaped precipitations, which increase in amount with the increasing sulphur content and are considered to be some sulphides of metals.

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The change of thermal dilatation during the aging process of 5 treated at various aging temperatures was observed and discussed. The result was compared with the previous result of the measurement on the temperature dependence of electrical resistance and it was found that the result supported the previous conclusion. The outstanding changes observed were that of contraction at 350 to 550°C, the great expansion at 550° to 650°C, and the change of expansion at 700 to 800°C; They vary with aging conditions. Thus, it was concluded that there are two different kinds of transformation mechanism during the aging process. One, which occurs below about 600°C may be something like order-disorder transition, and the other is a precipitation which occurs during the aging process above 650°C. It seems that the former mainly causes the best magnetic properties.

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An electron microscope study is made on isothermal decomposition in 8 alloy as annealed around 800°C for 10–90 min in a magnetic field. The results obtained are found to agree well in many essential aspects with Cahn’s theoretical predictions on spinodal decomposition in a ferromagnetic cubic alloy. In the case of 10-min annealing, the predicted linear relationship can be confirmed between a square of the wavenumber of the modulated structure and the decomposition temperature, and an extrapolation of the straight line yields a reasonable spinodal temperature T_s of 860°C. Furthermore, some interesting facts are found on the later stage decomposition: Within a period of 10 to 90 min, the wavelength, i.e. the particle size grows linearly with annealing time. And, when annealed at a higher temperature near the T_s, it decomposes into a three-phase structure, among which the least ferromagnetic phase only possesses a peculiar substructure. A tentative explanation is given for these facts.

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The magnetic properties of 5 magnet (8%Al, 14%Ni, 24%Co,3%Cu and Fe) depend sensitively on heat-treatment,that is cooling in magnetic field and subsequent aging. The changes of coercive force, residual induction, maximum energy products and powder patterns of the magnetic domain were observed during these processes. The coercive force (or residual induction) changes logarithmically with the cooling rate. This empirical relationship is satisfied with or without magnetic field when cooling from 1,000 to 700°. The changes of coercive force as a function of aging time after cooling in magnetic field can be expressed by Austin-Rickett’s formula. These results are explained qualitatively, if we consider that during cooling in magnetic field the nuclei of meta-stable phase are mainly formed and then the growth process takes place during subsequent aging. In the cooling rate between 0.8 and 7°/sec, the activation energy of subsequent aging process is 46,000±2,000 cal/mol which is independent of the cooling rate.

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In this report, fullness of the demagnetisation curve of " V" magnet was investigated. When the specimen is heated to 1300°C, cooled in a field of 1000 Oersted or over, at the rate 1-3°C/sec (700-900°C) and baked at 625°C, most preferable magnetic properties or curvature of demagnetization curve was obtained. It was concerned that the commercial magnet has a high residual induction and coercive force, but fullness of its demagnetization curve is small.

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The effect of Niobium (in the form of a 70% Niobium Fe-Nb alloy) added to a sintered permanent magnet alloy of the 5 type, (8.3% Al, 15% Ni, 24% Co, 3% Cu, the remainder Fe) has been studied, cpartiulary, in relation to their linear shrinkage, density, magnetic properties, transverse rupture strength, pore size, and microstructure. Experimental results indicate that the addition of 0.35∼0.70% of Niobium improves the qualtities of 5 type alloys prepared by sintering in pure Hydrogen, but large percentage additions causes pore aggregation, rapid grain growth, and detrimental effects on rupture strength and magnetic properties.

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8-type magnet alloys containing more than 5% Ti have been well-known to have very high coercive forces, particularly when the isothermal field treatment is applied. As a primary approach in this research to explore its cause, the transformations, microstructures and magnet characteristics were investigated in a series of 8-type alloys with various titanium contents. The critical temperatures of the transformations including magnetic transition were determined as a function of titanium content. It may be reasonably concluded that the mechanism of magnetic hardening in these alloys is similar to that in 5-type alloys containing no titanium.
It was shown that when the alloys were subjected to isothermal field treatment, the coercive fore obtained depended largely upon the temperature of the treatment, and slightly upon the treating time. In each of the specimens, the optimum temperature of the treatment was found to exist about 50°C below the critical temperature of the two-phase separation reaction and to raise as the titanium content was increased. In addition, the magnetic anisotropy induced by the heat treatments in a magnetic field seems rather to decrease in magnitude with increasing titanium content. Furthermore, the electron microscopic observation has revealed that the precipitate particles developed by the optimal treatment are likely to increase in both size and dimension ratio with increasing titanium content.

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Vibrational spectra of realistic structural models for ternary –– decagonal quasicrystals are studied. A bunch of dispersion-less modes is obtained above a few meV, which is extremely low in comparison with usual optic modes. Analyzing the local vibrational density of states at an individual atomic site, we identify several Al sites where low- and high-frequency vibrations are localized. The localized vibrations are attributed to the strong Al–TM interaction and the local atomic arrangements realized in the complex structures. Low-frequency dispersion-less modes are of special interest in relation to the phason degrees of freedom in QC but no signature of large atomic motion causing the phasonic tile flip is obtained in the low-frequency localized vibrational modes.

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Compression and sheath forging tests have been performed at high temperatures up to 1500 K for as-cast 5 and Sendust alloys which are brittle even at temperatures higher than T_m⁄2 (T_m: melting point). And the effects of various working factors and separation to dual phase on deformability, flow stress and microstructure of deformed materials have been examined.
A large compressive strain more than 1.5 was obtained for 5 in the temperature range from 1350 to 1600 K and for Sendust in the range from 1050 to 1500 K at a strain rate of 0.0011 s⁻¹.
Materials deformed in the ductile range showed homogeneous fine structure. In the case of the alloy, the ductile temperature range was extended to lower side by the separation to dual phase.
The deformability in the ductile range depended strongly on the strain rate, and at strain rates higher than 100 s⁻¹ grain boundary brittle fracture appeared in all specimens.
By the forging using a miled steel sheathed billet at a temperature of 1470 K and a strain rate of 1 s⁻¹, a forging ratio more than 7 was obtained for both materials without cracks.

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By using water-atomized Fe-Cr-Co powder, an influence of some elements such as Cr, Co, Si, S and B on densification and magnetic properties of Fe-Cr-Co magnets was investigated. The results were as follows.
(1) Magnetic properties of sintered Fe-Cr-Co magnets were expressed well by relation between Fe/Co and (Fe+Co)/Cr. Fe-Cr-Co system superior of remanence (B_r) were plotted on the extended line of the composition of type magnets such as Ticonal 2000, 8 and 5. Coercive force (H_c) tended to become higher with decreasing the ratio of (Fe+Co)/Cr.
(2) Silicon lowered the oxygen content in water-atomized Fe-Cr-Co powder and improved densification of compacts by sintering, where optimum silicon content was about 1%.
(3) Sulfur addition also improved densification of compacts by sintering. In the case of sulfur addition, magnetic properties were better than those of silicon addition, where optimum sulfur content was about 0.10∼0.20%.
(4) Sulfur and boron addition further improved densification of compacts by sintering and resultantly, magnetic properties.

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Saturation magnetization and coercive force of 5 and other magnet alloys with similar compositions are measured at elevated temperatures by means of an astatic magnetometer. The I-T curves obtained reveal that these alloys consist of two kinds of ferromagnetic phases, α₁ and α₂, after appropriate heat-treatment. It is found that Curie point of the less ferromagnetic phase α₂ changes considerably with aging temperature. These results are also discussed from the standpoint of an equilibrium diagram and the phase relation. Each of the H_c-T curves obtained shows a striking maximum at a certain temperature, which corresponds to the Curie point of the α₂ phase contained in the alloy. Particularly for a commercial alloy of 5 aged at about 600°C, the Curie point of the α₂ phase lies in the neighbourhood of room temperature, so that a maximum value of the coercive force can conveniently be obtained at room temperature. Furthermore, a theoretical approach is proposed to estimate the coercive force for such a two-phase alloy. This may satisfactorily explain the characteristic feature of the observed H_c–T curve, and may elucidate that the coercive force of 5 largely depends upon the magnetization of the less ferromagnetic matrix.

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